Semi-passive control of solidification in powdered materials

ABSTRACT

Disclosed herein are surface-functionalized powders which alter the solidification of the melted powders. Some variations provide a powdered material comprising a plurality of particles fabricated from a first material, wherein each of the particles has a particle surface area that is continuously or intermittently surface-functionalized with nanoparticles and/or microparticles selected to control solidification of the powdered material from a liquid state to a solid state. Other variations provide a method of controlling solidification of a powdered material, comprising melting at least a portion of the powdered material to a liquid state, and semi-passively controlling solidification of the powdered material from the liquid state to a solid state. Several techniques for semi-passive control are described in detail. The methods may further include creating a structure through one or more techniques selected from additive manufacturing, injection molding, pressing and sintering, capacitive discharge sintering, or spark plasma sintering.

PRIORITY DATA

This patent application is a non-provisional application with priorityto U.S. Provisional Patent App. No. 62/192,568, filed Jul. 15, 2015,which is hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention generally relates to powdered materials, objectscontaining such powdered materials, and methods of making and using thesame.

BACKGROUND OF THE INVENTION

Powder processing of metals includes capacitive discharge sintering,direct metal laser melting, electron beam melting, and other techniques.These processes have been used to create near net shape parts, andoccasionally to control microstructure. This microstructure control islimited to grain size and grain orientation control. This control is alldependent on heat input. What is desired is to control nucleation andgrowth kinetics within the structure independent of, or in conjunctionwith, thermal input.

Prior art exists in which nanoparticles are used in melts to help seedcrystallization. This is usually accomplished by adding nanoparticlesinto a molten alloy, physically distributing them, and then casting theresulting material. These nanoparticles are generally ceramic becausethey must be added and mixed in the melt. Metal particles and certaindesirable ceramic particles would likely be dissolved and thereforecannot be used in this prior-art process. The microstructures whichdevelop during such processing can be easily attributed to the castingprocess. The microstructures have nanoparticles segregated to theinterdendritic regions. See, for example, Chen et al., “Rapid Control ofPhase Growth by Nanoparticles,” Nature Communications, 5:3879, May 2014;and Xu et al., “Theoretical Study and Pathways for Nanoparticle Captureduring Solidification of Metal Melt,” Journal of Physics: CondensedMatter, 24 (2012) 255304.

There are no known methods to develop three-dimensional nanoparticlearchitectures within metal microstructures. These architectures couldsignificantly improve material properties by impeding, blocking, orredirecting dislocation motion in specific directions. This could beused to control failure mechanisms well beyond anything available inisotropic or anisotropic materials today.

Generally, improved methods of controlling solidification in powdermaterials, and compositions suitable for such methods, are needed.Preferably, the control of solidification does not require active,dynamic adjustment of reaction parameters during the solidificationprocess.

SUMMARY OF THE INVENTION

The present invention addresses the aforementioned needs in the art, aswill now be summarized and then further described in detail below.

Some variations provide a powdered material comprising a plurality ofparticles, wherein the particles are fabricated from a first material,and wherein each of the particles has a particle surface area that issurface-functionalized with a second material containing nanoparticlesand/or microparticles selected to control solidification of the powderedmaterial from a liquid state to a solid state. The surfacefunctionalization may be continuous or intermittent (i.e. discontinuousacross the surface).

In some embodiments, the powdered material is characterized in that onaverage at least 1% or at least 10% of the particle surface area issurface-functionalized with the nanoparticles and/or the microparticles.

The particles may be present as a loose powder, a paste, a suspension, agreen body, or a combination thereof. The particles may have an averageparticle size from about 1 micron to about 1 centimeter. In someembodiments, the first material is selected from the group consisting ofceramic, metal, polymer, glass, and combinations thereof.

The nanoparticles and/or microparticles have an average maximum particledimension from about 1 nanometer to about 100 microns. In someembodiments, the average maximum particle dimension is less than 100nanometers. In these or other embodiments, the nanoparticles and/ormicroparticles have an average minimum particle dimension from about 1nanometer to about 1 micron, such as less than 100 nanometers.

The nanoparticles and/or microparticles may be fabricated from a secondmaterial selected from the group consisting of metal, ceramic, polymer,carbon, and combinations thereof. The first material and the secondmaterial may compositionally be the same or different.

Other variations provide a method of controlling solidification of apowdered material, the method comprising:

providing a powdered material comprising a plurality of particles,wherein the particles are fabricated from a first material, and whereineach of the particles has a particle surface area that issurface-functionalized with a second material containing nanoparticlesand/or microparticles;

melting at least a portion of the powdered material to a liquid state;and

semi-passively controlling solidification of the powdered material fromthe liquid state to a solid state.

The particles, prior to the melting, may be present as a loose powder, apaste, a suspension, a green body, or a combination thereof, forexample. In some embodiments, at least 2 vol % or at least 10 vol % ofthe powdered material is melted to form the liquid state.

The particles of first material may have an average particle size fromabout 1 micron to about 1 centimeter. The first material may be selectedfrom the group consisting of ceramic, metal, polymer, glass, andcombinations thereof. The second material (nanoparticles and/ormicroparticles) may be fabricated from a selected from the groupconsisting of metal, ceramic, polymer, carbon, and combinations thereof.

There are various types of semi-passive control of solidification. Insome embodiments, semi-passively controlling solidification includesnucleation control. In these or other embodiments, semi-passivelycontrolling solidification includes thermodynamic control. In these orother embodiments, semi-passively controlling solidification includesthermal conductivity control. In certain embodiments, semi-passivelycontrolling solidification includes eutectic or peritectic reactioncontrol. In any of these or other embodiments, semi-passivelycontrolling solidification includes rejection of contaminants reactedwith the nanoparticles and/or microparticles.

In some embodiments, the solid state is a three-dimensionalmicrostructure containing the nanoparticles and/or microparticles asinclusions distributed throughout the solid state.

In some embodiments, the solid state is a layered microstructurecontaining one or more layers comprising the nanoparticles and/ormicroparticles.

The method may further include creating a structure through one or moretechniques selected from the group consisting of additive manufacturing,injection molding, pressing and sintering, capacitive dischargesintering, and spark plasma sintering. The present invention provides asolid object or article comprising a structure produced by a processcomprising such a method.

Some variations provide a solid object or article comprising at leastone solid phase (i) containing a powdered material as described, or (ii)derived from a liquid form of a powdered material as described. Thesolid phase may form from 0.25 wt % to 100 wt % of the solid object orarticle, for example.

Other variations of the invention provide a solid object or articlecomprising a continuous solid phase and a three-dimensional network ofnanoparticle and/or microparticle inclusions distributed throughout thecontinuous solid phase, wherein the three-dimensional network blocks,impedes, or redirects dislocation motion within the solid object orarticle.

In some embodiments, the nanoparticle and/or microparticle inclusionsare distributed uniformly throughout the continuous solid phase. Thenanoparticle and/or microparticle inclusions may be present at aconcentration from about 0.1 wt % to about 50 wt % of the solid objector article.

The nanoparticles and/or microparticles may have an average maximumparticle dimension less than 100 nanometers, an average minimum particledimension less than 100 nanometers, or both of these.

The solid phase may be fabricated from a first material selected fromthe group consisting of ceramic, metal, polymer, glass, and combinationsthereof. The nanoparticles and/or microparticles may be fabricated froma second material selected from the group consisting of metal, ceramic,polymer, carbon, and combinations thereof. The second material may bethe same as or different than the composition of the solid phase.

BRIEF DESCRIPTION OF THE DRAWINGS

The schematic drawings herein represent surface-functionalizationpatterns and final microstructures which may be achieved in embodimentsof the invention. These drawings should not be construed as limiting inany way. It is also noted that illustrations contained in the drawingsare not drawn to scale and various degrees of zooming-in are employedfor purposes of understanding these embodiments.

FIG. 1 is a schematic illustration of surface-functionalized powderparticles with either a single type of nanoparticle or multiple types ofnanoparticles coated onto the surface of the particles.

FIG. 2A is a schematic illustration of semi-passive solidificationcontrol including nucleation control, in which nanoparticles act asnucleation sites which lead to equiaxed grains in the final solidmaterial.

FIG. 2B is a schematic illustration of semi-passive solidificationcontrol including nucleation control, in which nanoparticles preventrunaway growth of individual dendrites, leading to equiaxed grains inthe final solid material.

FIG. 3 is a schematic illustration of semi-passive solidificationcontrol including peritectic reactions of dissolved nanoparticles uponcooling, leading to nanoparticle formation of dispersoids.

FIG. 4 is a schematic illustration of semi-passive solidificationcontrol in which a melt solidifies with limited movement of assemblednanoparticles, thereby allowing the nanoparticles to orient in athree-dimensional structure which repeats throughout the final solidmaterial.

FIG. 5A is a schematic illustration of semi-passive solidificationcontrol including thermodynamic control, in which nanoparticles react inthe melt and the reaction enthalpy is utilized to control heat flowduring solidification.

FIG. 5B is a schematic illustration of semi-passive solidificationcontrol including thermodynamic control, in which nanoparticles or areaction product thereof are driven to the surface, where vaporizationremoves heat from the system.

FIG. 6A is a schematic illustration of semi-passive solidificationcontrol including conductivity or emissivity control, in whichnanoparticles driven to the surface form a layer with a differentconductivity or emissivity than the underlying material.

FIG. 6B is a schematic illustration of semi-passive solidificationcontrol including conductivity or emissivity control, in whichnanoparticles remain distributed and change the conductivity of the meltand the final solid material.

FIG. 7A is a schematic illustration of semi-passive solidificationcontrol including contaminant removal and rejection to the surface.

FIG. 7B is a schematic illustration of semi-passive solidificationcontrol including contaminant reaction, in which the reactedcontaminants remain in the solid.

FIG. 8 is a schematic illustration of surface melting of afunctionalized powder particle, in which heat is applied and thenanoparticles react with the surface to form a melt in less than 100% ofthe particle volume.

FIG. 9 is a schematic illustration of the formation of a layeredcomposite structure, in which a functionalized powder having twodifferent types of nanoparticles leads to different particlesegregation, resulting in a layered structure.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The compositions, structures, systems, and methods of the presentinvention will be described in detail by reference to variousnon-limiting embodiments.

This description will enable one skilled in the art to make and use theinvention, and it describes several embodiments, adaptations,variations, alternatives, and uses of the invention. These and otherembodiments, features, and advantages of the present invention willbecome more apparent to those skilled in the art when taken withreference to the following detailed description of the invention inconjunction with the accompanying drawings.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contextclearly indicates otherwise. Unless defined otherwise, all technical andscientific terms used herein have the same meaning as is commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs.

Unless otherwise indicated, all numbers expressing conditions,concentrations, dimensions, and so forth used in the specification andclaims are to be understood as being modified in all instances by theterm “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the following specification andattached claims are approximations that may vary depending at least upona specific analytical technique.

The term “comprising,” which is synonymous with “including,”“containing,” or “characterized by” is inclusive or open-ended and doesnot exclude additional, unrecited elements or method steps. “Comprising”is a term of art used in claim language which means that the named claimelements are essential, but other claim elements may be added and stillform a construct within the scope of the claim.

As used herein, the phrase “consisting of” excludes any element, step,or ingredient not specified in the claim. When the phrase “consists of”(or variations thereof) appears in a clause of the body of a claim,rather than immediately following the preamble, it limits only theelement set forth in that clause; other elements are not excluded fromthe claim as a whole. As used herein, the phrase “consisting essentiallyof” limits the scope of a claim to the specified elements or methodsteps, plus those that do not materially affect the basis and novelcharacteristic(s) of the claimed subject matter.

With respect to the terms “comprising,” “consisting of,” and “consistingessentially of,” where one of these three terms is used herein, thepresently disclosed and claimed subject matter may include the use ofeither of the other two terms. Thus in some embodiments not otherwiseexplicitly recited, any instance of “comprising” may be replaced by“consisting of” or, alternatively, by “consisting essentially of.”

Variations of this invention are predicated on the discovery of methods,compositions, and systems which can control the solidification of powdermaterials. This discovery is of particular interest in the field ofadditive manufacturing (also known as 3D printing) in whichsolidification is poorly understood. Controlling solidification can havea drastic impact on microstructure and thus material properties (e.g.strength, toughness). In some cases faster solidification is desirable;while in other cases slow solidification may produce the desiredmicrostructure. In certain cases it is not desirable to fully melt thepowder; but rather to melt and solidify only at the powder surface. Thisinvention provides routes to control—in both time andspace—solidification in materials, utilizing surface functionalizationof the primary powder being processed.

In particular, some variations provide routes to controlledsolidification of materials which are generally difficult or impossibleto process otherwise. The principles disclosed herein may be applied toadditive manufacturing as well as joining techniques, such as welding.Certain unweldable metals, such as high-strength aluminum alloys (e.g.,aluminum alloys 7075, 7050, or 2199) would be excellent candidates foradditive manufacturing but normally suffer from hot cracking. Themethods disclosed herein allow these alloys to be processed withsignificantly reduced cracking tendency.

Proper control of solidification can lead to greater part reliabilityand enhanced yield. Some embodiments of the invention provide powdermetallurgy—processed parts that are equivalent to machined parts. Someembodiments provide corrosion-resistant surface coatings that are formedduring the part fabrication instead of as an extra step.

This disclosure describes control of nucleation and growth kineticswithin the structure independent of, or in conjunction with, thermalinput. This disclosure describes methods which incorporate phase andstructure control to generate three-dimensional microstructuralarchitecture. Methods for inclusion/contaminant removal are provided, aswell as development of composite structures.

Variations of this invention are premised on controlling solidificationthrough limiting or increasing thermal conductivity and/or radiationwith the surroundings, utilizing enthalpies of formation and varyingheat capacities to control thermal loads during solidification, and/orutilizing surface tension to control entrapment of desired species—orrejection of undesired species—in the final solidification product.

Some variations provide methods to control nanoparticle (ormicroparticle)/material segregation. When rapid solidificationtechniques are applied to powder processing, a unique microstructure maybe developed, independent of the cast structure. Likewise, theconfiguration of the nanoparticles or microparticles around theparticles prior to melting may introduce a three-dimensionalnanoparticle architecture within the overall microstructure.

Embodiments of this invention provide three-dimensional nanoparticlearchitectures within metal microstructures. Not wishing to be bound bytheory, these architectures may significantly improve the materialproperties by impeding, blocking, or redirecting dislocation motion inspecific directions. This discovery could be used to control failuremechanisms beyond prior-art isotropic or anisotropic materials.

The present invention is not limited to metallic materials and canprovide similar benefits with a significantly less difficult, morerepeatable, and energy-efficient production method. The semi-passivenature of the process typically requires no alteration of existingtooling and can be employed in existing manufacturing settings.

Powder materials are the general feedstock for a powder metallurgy (orsimilar) process, including but not limited to additive manufacturing,injection molding, and press and sintered applications. As intendedherein, “powder materials” refers to any powdered ceramic, metal,polymer, glass, or composite or combination thereof. In someembodiments, the powder materials are metals or metal-containingcompounds, but this disclosure should not be construed as limited tometal processing. Powder sizes are typically between about 1 micron andabout 1 mm, but in some cases could be as much as about 1 cm.

The powdered material may be in any form in which discrete particles canbe reasonably distinguished from the bulk. The powder materials are notalways observed as loose powders and may be present as a paste,suspension, or green body. A green body is an object whose mainconstituent is weakly bound powder material, before it has been meltedand solidified. For instance, a filler rod for welding may consist ofthe powder material compressed into a usable rod.

Particles may be solid, hollow, or a combination thereof. Particles canbe made by any means including, for example, gas atomization, milling,cryomilling, wire explosion, laser ablation, electrical-dischargemachining, or other techniques known in the art. The powder particlesmay be characterized by an average aspect ratio from about 1:1 to about100:1. The “aspect ratio” means the ratio of particle length to width,expressed as length:width. A perfect sphere has an aspect ratio of 1:1.For a particle of arbitrary geometry, the length is taken to be themaximum effective diameter and the width is taken to be the minimumeffective diameter.

In some embodiments, the particles are in the shape of rods. By “rod” ismeant a rod-shaped particle or domain shaped like long sticks, dowels,or needles. The average diameter of the rods may be selected from about5 nanometers to about 100 microns, for example. Rods need not be perfectcylinders, i.e. the axis is not necessarily straight and the diameter isnot necessarily a perfect circle. In the case of geometrically imperfectcylinders (i.e. not exactly a straight axis or a round diameter), theaspect ratio is the actual axial length, along its line of curvature,divided by the effective diameter, which is the diameter of a circlehaving the same area as the average cross-sectional area of the actualnanorod shape.

The powder material particles may be anisotropic. As meant herein,“anisotropic” particles have at least one chemical or physical propertythat is directionally dependent. When measured along different axes, ananisotropic particle will have some variation in a measurable property.The property may be physical (e.g., geometrical) or chemical in nature,or both. The property that varies along multiple axes may simply be thepresence of mass; for example, a perfect sphere would be geometricallyisotropic while a cylinder is geometrically anisotropic. The amount ofvariation of a chemical or physical property may be 5%, 10%, 20%, 30%,40%, 50%, 75%, 100% or more.

“Solidification” generally refers to the phase change from a liquid to asolid. In some embodiments, solidification refers to a phase changewithin the entirety of the powder volume. In other embodiments,solidification refers to a phase change at the surface of the particlesor within a fractional volume of the powder material. In variousembodiments, at least (by volume) 1%, 2%, 5%, 10%, 15%, 20%, 25%, 30%,40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, or 100% of the powdered materialis melted to form the liquid state. In certain embodiments, from about1% to about 90% (by volume) of the powdered material is melted to formthe liquid state. In certain embodiments, from about 2% to about 50% (byvolume) of the powdered material is melted to form the liquid state. Incertain embodiments, from about 50% to 100% (by volume) of the powderedmaterial is melted to form the liquid state.

For a metal or mixtures of metals, solidification generally results inone or more solid metal phases that are typically crystalline, butsometimes amorphous. Ceramics also may undergo crystallinesolidification or amorphous solidification. Metals and ceramics may forman amorphous region coinciding with a crystalline region (e.g., insemicrystalline materials). In the case of certain polymers and glasses,solidification may not result in a crystalline solidification. In theevent of formation of an amorphous solid from a liquid, solidificationrefers to a transition of the liquid from above the glass-transitiontemperature to an amorphous solid at or below the glass-transitiontemperature. The glass-transition temperature is not alwayswell-defined, and sometimes is characterized by a range of temperatures.

“Functionalization” or “surface functionalization” refers to a surfacemodification on the powdered materials, which modification significantlyaffects the solidification behavior (e.g., solidification rate, yield,selectivity, heat release, etc.) of the powder materials. In variousembodiments, a powdered material is functionalized with about 1%, 2%,5%, 10%, 15%, 20%, 25%, 30%, 40%, 50%, 60%, 70%, 80%, 85%, 90%, 95%,99%, or 100% of the surface area of the powdered material having thesurface-functionalization modifications. The surface modification maybea surface-chemistry modification, a physical surface modification, or acombination thereof.

In some embodiments, the surface functionalization includes ananoparticle coating and/or a microparticle coating. The nanoparticlesand/or microparticles may include a metal, ceramic, polymer, or carbon,or a composite or combination thereof. The surface functionalization mayinclude a particle assembly that is chemically or physically disposed onthe surface of the powder materials.

FIG. 1 is a schematic illustration of surface-functionalized powderparticles 100 with either a single type of nanoparticle 110 or multipletypes of nanoparticles 110, 115 coated onto the surface of the particles100. Methods of producing surface-functionalized powder materials, insome embodiments, are further discussed below. The powder particles 100may include ceramic, metal, polymer, glass, or combinations thereof.Nanoparticles 110, 115 may include metal, ceramic, polymer, carbon, orcombinations thereof. Specific material examples are described below.

Due to the small size of nanoparticles and their reactivity, thebenefits provided herein may be possible with less than 1% surface areacoverage. In the case of functionalization with a nanoparticle of thesame composition as the base powder, a surface-chemistry change may notbe detectible and can be characterized by topological differences on thesurface, for example. Functionalization with a nanoparticle of the samecomposition as the base powder may be useful to reduce the melting pointin order to initiate sintering at a lower temperature, for example.

In some embodiments, microparticles coat micropowders or macropowders.The micropowder or macropowder particles may include ceramic, metal,polymer, glass, or combinations thereof. The microparticles (coating)may include metal, ceramic, polymer, carbon, or combinations thereof. Inthe case of microparticles coating other micropowders or macropowders,functionalization preferably means that the coating particles are ofsignificantly different dimension(s) than the base powder. For example,the microparticles may be characterized by an average dimension (e.g.,diameter) that is less than 20%, 10%, 5%, 2%, or 1% of the largestdimension of the coated powders.

In some embodiments, the surface functionalization is in the form of acontinuous coating or an intermittent coating. A continuous coatingcovers at least 90% of the surface, such as about 95%, 99%, or 100% ofthe surface (recognizing there may be defects, voids, or impurities atthe surface). An intermittent coating is non-continuous and covers lessthan 90%, such as about 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, 2%,1%, or less of the surface. An intermittent coating may be uniform(e.g., having a certain repeating pattern on the surface) or non-uniform(e.g., random).

In general, the coating may be continuous or discontinuous. The coatingmay have several characteristic features. In one embodiment, the coatingmay be smooth and conformal to the underlying surface. In anotherembodiment, the coating may be nodular. The nodular growth ischaracteristic of kinetic limitations of nucleation and growth. Forexample, the coating may look like cauliflower or a small fractalgrowing from the surface. These features can be affected by theunderling materials, the method of coating, reaction conditions, etc.

A coating may or may not be in the form of nanoparticles ormicroparticles. That is, the coating may be derived from nanoparticlesor microparticles, while discrete nanoparticles or microparticles may nolonger be present. Various coating techniques may be employed, such as(but not limited to) electroless deposition, immersion deposition, orsolution coating. The coating thickness is preferably less than about20% of the underlying particle diameter, such as less than 15%, 10%, 5%,2%, or 1% of the underlying particle diameter.

In some embodiments, the surface functionalization also includes directchemical or physical modification of the surface of the powdermaterials, such as to enhance the bonding of the nanoparticles ormicroparticles. Direct chemical modification of the surface of thepowder materials, such as addition of molecules, may also be utilized toaffect the solidification behavior of the powder materials. A pluralityof surface modifications described herein may be used simultaneously.

As intended herein, “nanoparticles” refer to particles with the largestdimension between about 1 nm and 1000 nm. A preferred size ofnanoparticles is less than 250 nm, more preferably less than 100 nm. Asintended herein, “microparticles” refer to particles with the largestdimension between about 1 micron and 100 microns. Nanoparticles ormicroparticles may be metal, ceramic, polymer, carbon-based, orcomposite particles, for example. The nanoparticle or microparticle sizemay be determined based on the desired properties and final function ofthe assembly.

Nanoparticles or microparticles may be spherical or of arbitrary shapewith the largest dimension typically not exceeding the above largestdimensions. An exception is structures with extremely high aspectratios, such as carbon nanotubes in which the dimensions may include upto 100 microns in length but less than 100 nm in diameter. Thenanoparticles or microparticles may include a coating of one or morelayers of a different material. Mixtures of nanoparticles andmicroparticles may be used. In some embodiments, microparticlesthemselves are coated with nanoparticles, and themicroparticle/nanoparticle composite is incorporated as a coating orlayer on the powder material particles.

Some variations provide a powdered material comprising a plurality ofparticles, wherein the particles are fabricated from a first material(e.g., ceramic, metal, polymer, glass, or combinations thereof), andwherein each of the particles has a particle surface area that issurface-functionalized (such as continuously or intermittently) withnanoparticles and/or microparticles selected to control solidificationof the powdered material from a liquid state to a solid state. Thenanoparticles and/or microparticles may include metal, ceramic, polymer,carbon, or combinations thereof.

In some embodiments, the powdered material is characterized in that onaverage at least 1%, 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%,50%, or more of the particle surface area is surface-functionalized withthe nanoparticles and/or the microparticles.

In some embodiments, the nanoparticles and/or microparticles areselected to control solidification of a portion of the powderedmaterial, such as a region of powdered material for which solidificationcontrol is desired. Other regions containing conventional powderedmaterials, without nanoparticles and/or microparticles, may be present.In some embodiments, the nanoparticles and/or microparticles areselected to control solidification of a portion of each the particles(e.g., less than the entire volume of a particle, such as an outershell).

Various material combinations are possible. In some embodiments, thepowder particles are ceramic and the nanoparticles and/or microparticlesare ceramic. In some embodiments, the powder particles are ceramic andthe nanoparticles and/or microparticles are metallic. In someembodiments, the powder particles are polymeric and the nanoparticlesand/or microparticles are metallic, ceramic, or carbon-based. In someembodiments, the powder particles are glass and the nanoparticles and/ormicroparticles are metallic. In some embodiments, the powder particlesare glass and the nanoparticles and/or microparticles are ceramic. Insome embodiments, the powder particles are ceramic or glass and thenanoparticles and/or microparticles are polymeric or carbon-based, andso on.

Exemplary ceramic materials for the powders, or the nanoparticles and/ormicroparticles, include (but are not limited to) SiC, HfC, TaC, ZrC,NbC, WC, TiC, TiC_(0.7)N_(0.3), VC, B₄C, TiB₂, HfB₂, TaB₂, ZrB₂, WB₂,NbB₂, TaN, HfN, BN, ZrN, TiN, NbN, VN, Si₃N₄, Al₂O₃, MgAl₂O₃, HfO₂,ZrO₂, Ta₂O₅, TiO₂, SiO₂, and oxides of rare-earth elements Y, La, Ce,Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho Er, Tm, Yb, and/or Lu.

Exemplary metallic materials for the powders, or the nanoparticlesand/or microparticles, include (but are not limited to) Sc, Ti, V, Cr,Y, Zr, Nb, Mo, Ru, Rh, Pd, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho Er,Tm, Yb, Lu, Ta, W, Re, Os, Ir, Pt, Si, or B.

Exemplary polymer materials for the powders, or the nanoparticles and/ormicroparticles, include (but are not limited to) thermoplastic organicor inorganic polymers, or thermoset organic or inorganic polymers.Polymers may be natural or synthetic.

Exemplary glass materials for the powders include (but are not limitedto) silicate glasses, porcelains, glassy carbon, polymer thermoplastics,metallic alloys, ionic liquids in a glassy state, ionic melts, andmolecular liquids in a glassy state.

Exemplary carbon or carbon-based materials for the nanoparticles and/ormicroparticles include (but are not limited to) graphite, activatedcarbon, graphene, carbon fibers, carbon nanostructures (e.g., carbonnanotubes), and diamond (e.g., nanodiamonds).

These categories of materials are not mutually exclusive; for example agiven material may be metallic/ceramic, a ceramic glass, a polymericglass, etc.

The selection of the coating/powder composition will be dependent on thedesired properties and should be considered on a case-by-case basis.Someone skilled in the art of material science or metallurgy will beable to select the appropriate materials for the intended process, basedon the information provided in this disclosure. The processing and finalproduct configuration should also be dependent on the desiredproperties. Someone skilled in the art of material science, metallurgy,and/or mechanical engineering will be able to select the appropriateprocessing conditions for the desired outcome, based on the informationprovided in this disclosure.

In some embodiments, a method of controlling solidification of apowdered material comprises:

providing a powdered material comprising a plurality of particles,wherein the particles are fabricated from a first material, and whereineach of the particles has a particle surface area that issurface-functionalized with nanoparticles and/or microparticles;

melting at least a portion of the powdered material to a liquid state;and

semi-passively controlling solidification of the powdered material fromthe liquid state to a solid state.

As intended in this description, “semi-passive control,” “semi-passivelycontrolling,” and like terminology refer to control of solidificationduring heating, cooling, or both heating and cooling of thesurface-functionalized powder materials, wherein the solidificationcontrol is designed prior to melting through selected functionalizationand is not actively controlled externally once the melt-solidificationprocess has begun. Note that external interaction is not necessarilyavoided. In some embodiments, semi-passive control of solidificationfurther includes selecting the atmosphere (e.g., pressure, humidity, orgas composition), temperature, or thermal input or output. These factorsas well as other factors known to someone skilled in the art may or maynot be included in semi-passive control.

Exemplary semi-passive control processes, enabled through surfacefunctionalization as described herein, will now be illustrated.

One route to control nucleation is the introduction, into the liquidphase, of nanoparticles derived from a coating described above. Thenanoparticles may include any material composition described above andmay be selected based on their ability to wet into the melt. Upon meltinitiation, the nanoparticles wet into the melt pool as dispersedparticles which, upon cooling, serve as nucleation sites, therebyproducing a fine-grained structure with observable nucleation sites inthe cross-section. In some embodiments, the density of nucleation sitesis increased, which may increase the volumetric freezing rate due to thenumber of growing solidification fronts and the lack of a nucleationenergy barrier.

In an exemplary embodiment, ceramic nanoparticles, e.g. TiB₂ or Al₂O₃nanoparticles, are coated onto aluminum alloy microparticles. Theceramic nanoparticles are introduced into an aluminum alloy melt pool inan additive manufacturing process. The nanoparticles then disperse inthe melt pool and act as nucleation sites for the solid. The additionalwell-dispersed nucleation sites can mitigate shrinkage cracks (hotcracking). Shrinkage cracks typically occur when liquid cannot reachcertain regions due to blockage of narrow channels between solidifyinggrains. An increase in nucleation sites can prevent formation of long,narrow channels between solidifying grains, because multiple smallgrains are growing, instead of few large grains.

In another exemplary embodiment, nanoparticles act as nucleation sitesfor a secondary phase in an alloy. The nanoparticles may comprise thesecondary phase or a material that nucleates the secondary phase (due tosimilar crystal structures, for instance). This embodiment can bebeneficial if the secondary phase is responsible for blockinginterdendritic channels leading to hot cracking. By nucleating manysmall grains of the secondary phase, a large grain that might block thenarrow channel between the dendrites can be avoided. Furthermore, thisembodiment can be beneficial if the secondary phase tends to form acontinuous phase between the grains of the primary phase, which promotesstress corrosion cracking. By providing additional nucleation sites forthe secondary phase, this secondary phase may be broken up andinterdispersed, preventing it from forming a continuous phase betweengrains of the primary alloy. By breaking up a secondary phase duringsolidification, there is the potential to more completely homogenize thematerial during heat treatment, which can decrease the likelihood ofstress corrosion cracking (fewer gradients in the homogenized material).If the secondary phase is not continuous, long notches from corrosionare less likely.

In another embodiment of nucleation control, the functionalized surfacemay fully or partially dissolve in the melt and undergo a reaction withmaterials in the melt to form precipitates or inclusions, which may actin the same manner as the nanoparticles in the preceding paragraph. Forexample, titanium particles may be coated on an aluminum alloy particle,which upon melting would dissolve the titanium. However, on cooling thematerial undergoes a peritectic reaction, forming aluminum-titaniumintermetallic (Al₃Ti) inclusions which would serve as nucleation sites.

In another embodiment, the coating may react with impurities to formnucleation sites. An example is a magnesium coating on a titanium alloypowder. Titanium has a very high solubility of oxygen (a commonatmospheric contaminant), which can affect the overall properties. Acoating of magnesium reacts within the melt, binding to dissolved oxygenwhich forms magnesium oxide (MgO) inclusions, promoting nucleation.

FIG. 2A is a schematic illustration of semi-passive solidificationcontrol including nucleation control, in which nanoparticles 210 (coatedonto powder particles 200) act as nucleation sites which lead toequiaxed grains 220 in the final solid material. The powder particles200 may include ceramic, metal, polymer, glass, or combinations thereof.Nanoparticles 210 may include metal, ceramic, polymer, carbon, orcombinations thereof.

FIG. 2B is a schematic illustration of semi-passive solidificationcontrol including nucleation control, in which nanoparticles 210 preventrunaway growth of individual dendrites, leading to equiaxed grains 220in the final solid material. Again, the powder particles 200 may includeceramic, metal, polymer, glass, or combinations thereof. Nanoparticles210 may include metal, ceramic, polymer, carbon, or combinationsthereof.

Nucleation control may include the use of ceramic particles. In someembodiments, the ceramic particles can be wet by the molten material,while in other embodiments, the ceramic particles cannot be wet by themolten material. The ceramic particles may be miscible or immisciblewith the molten state. The ceramic particles may be incorporated intothe final solid material. In some embodiments, the ceramic particles arerejected from the solid. Exemplary ceramic materials include (but arenot limited to) SiC, HfC, TaC, ZrC, NbC, WC, TiC, TiC_(0.7)N_(0.3), VC,B₄C, TiB₂, HfB₂, TaB₂, ZrB₂, WB₂, NbB₂, TaN, HfN, BN, ZrN, TiN, NbN, VN,Si₃N₄, Al₂O₃, MgAl₂O₃, HfO₂, ZrO₂, Ta₂O₅, TiO₂, SiO₂, and oxides ofrare-earth elements Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho Er, Tm,Yb, and/or Lu.

Nucleation control may include the use of metallic particles. In someembodiments, the metallic particles can be wet by the molten material.The metallic particles may form an alloy with the molten materialthrough a eutectic reaction or peritectic reaction. The alloy may be anintermetallic compound or a solid solution. In some embodiments, themetallic particles cannot be wet by the molten material and cannot forman alloy with the molten material. Exemplary metallic materials include(but are not limited to) Sc, Ti, V, Cr, Y, Zr, Nb, Mo, Ru, Rh, Pd, La,Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho Er, Tm, Yb, Lu, Ta, W, Re, Os, Ir,Pt, Si, or B.

Nucleation control may include the use of plastic particles. In someembodiments, the plastic particles can be wet by the molten material,while in other embodiments, the plastic particles cannot be wet by themolten material.

Nanoparticles promote surface growth of crystals that have goodepitaxial fit. Nucleation on the surface of a nanoparticle is morelikely when there is good fit between the crystal lattice parameters ofthe nanoparticles and the solidifying material. Nanoparticles may beselected to promote nucleation of a specific phase in the melt.

Generally, nucleation-promoting chemical reactions are dependent on theselected surface functionalization and on the heating (or cooling)parameters.

As nanoparticles or microparticles are organized on a particle surfaceunder conditions for which rapid melting or near melting occurs andrapidly fuses the particles together with very little melt convection,the coating will not have the time or associated energy to diffuse awayfrom its initial position relative to the other powders. This would inturn create a three-dimensional network structure of inclusions. Thus, amethod is provided to control maximum grain size and/or to design apredictable microstructure. The microstructure is dependent on theinitial powder size, shape, and packing configuration/density. Adjustingthe coating and powder parameters allows control of this hierarchicalstructure. In some embodiments, these architectures significantlyimprove material properties by impeding, blocking, or redirectingdislocation motion in specific directions, thereby reducing oreliminating failure mechanisms.

Utilizing the appropriate functionalization, the heat flow duringsolidification may be controlled using appropriate heats of fusion orvaporization. In some embodiments, inclusions are pulled into the meltor reacted within the melt (as described above). In some embodiments, acoating is rejected to the surface of the melt pool. Utilizing afunctionalization surface with a high vapor pressure at the desiredmelting point of the powder, vaporization would occur, resulting in acooling effect in the melt which increases the freezing rate. Asdescribed above, magnesium on a titanium alloy may accomplish this, inaddition to forming oxide inclusions. The effect of this is easilydetectible when comparing non-functionalized powders to functionalizedpowders under identical conditions, as well as comparing the compositionof feed material versus the composition of the final product.

In another embodiment, the opposite effect occurs. Some systems mayrequire slower solidification times than can be reasonably provided in acertain production system. In this instance, a higher-melting-pointmaterial, which may for example be rejected to the surface, freezes.This releases the heat of fusion into the system, slowing the total heatflux out of the melt. Heat may also be held in the melt to slowsolidification by incorporating a secondary material with asignificantly higher heat capacity.

In another embodiment, the heat of formation is used to control heatflow during melt pool formation and/or solidification. For example,nickel microparticles may be decorated with aluminum nanoparticles. Uponsupply of enough activation energy, the exothermic reaction of Ni and Alto NiAl is triggered. In this case, a large heat of formation isreleased (−62 kJ/mol) which may aid in melting the particles fully orpartially. The resulting NiAl intermetallic is absorbed into the meltand stays suspended as a solid (a portion may be dissolved) due to itshigher melting point, thereby acting as a nucleation site as well ashaving a strengthening effect on the alloy later.

Thermodynamic control of solidification may utilizenanoparticles/microparticles or surface coatings which undergo a phasetransformation that is different from phase transformations in the basematerial. The phase transformations may occur at different solidusand/or liquidus temperatures, at similar solidus and/or liquidustemperatures, or at the same solidus and/or liquidus temperatures. Thephase-transformed nanoparticles/microparticles or surface coatings maybe incorporated into the final solid material, or may be rejected fromthe final solid material, or both of these. The phase-transformednanoparticles/microparticles or surface coatings may be miscible orimmiscible with the molten state. The phase-transformednanoparticles/microparticles or surface coatings may be miscible orimmiscible with the solid state.

Thermodynamic control of solidification may utilizenanoparticles/microparticles or surface coatings which vaporize orpartially vaporize. For example, such coatings may comprise organicmaterials (e.g., waxes, carboxylic acids, etc.) or inorganic salts(e.g., MgBr₂, ZnBr₂, etc.)

Thermodynamic control of solidification may utilizenanoparticles/microparticles or surface coatings which release or absorbgas (e.g., oxygen, hydrogen, carbon dioxide, etc.).

Thermodynamic control of solidification may utilizenanoparticles/microparticles or surface coatings with different heatcapacities than the base material.

In addition to controlling the energy within the system, it also ispossible to control the rate at which heat leaves the system bycontrolling thermal conductivity or emissivity (thermal IR radiation).This type of control may be derived from a rejection to the surface orfrom the thermal conductivity of a powder bed during additivemanufacturing, for instance. In one embodiment, the functionalizationmay reject to the surface a low-conductivity material, which may be thefunctionalization material directly or a reaction product thereof, whichinsulates the underlying melt and decreases the freezing rate. In otherembodiments, a layer may have a high/low emissivity which wouldincrease/decrease the radiative heat flow into or out of the system.These embodiments are particularly applicable in electron-beam systemswhich are under vacuum and therefore radiation is a primary heat-flowmechanism.

FIG. 5A is a schematic illustration of semi-passive solidificationcontrol including thermodynamic control, in which nanoparticles 510react in the melt 530 and the reaction enthalpy is utilized to controlheat flow during solidification. The powder particles 500 may includeceramic, metal, polymer, glass, or combinations thereof. Nanoparticles510 may include metal, ceramic, polymer, carbon, or combinationsthereof. After the nanoparticles 510 react in the melt 530, along withcontrol of heat flow, new nanoparticles 540 may arise uponsolidification to solid material 550.

FIG. 5B is a schematic illustration of semi-passive solidificationcontrol including thermodynamic control, in which nanoparticles 510 or areaction product thereof are driven to the surface of the melt 530,where vaporization removes heat from the solidified material 550.Nanoparticles may be present at the surface as a layer 570, for example.Again, the powder particles 500 may include ceramic, metal, polymer,glass, or combinations thereof. Nanoparticles 510 may include metal,ceramic, polymer, carbon, or combinations thereof.

Additionally, in laser sintering systems, the emissivity of a rejectedlayer may be used to control the amount of energy input to the powderbed for a given wavelength of laser radiation. In another embodiment,the functionalized surface may be fully absorbed in the melt yet theproximity to other non-melted functionalized powders, such as additivemanufacturing in a powder bed, may change the heat conduction out of thesystem. This may manifest itself as a low-thermal-conductivity basepowder with a high-conductivity coating.

FIG. 6A is a schematic illustration of semi-passive solidificationcontrol including conductivity or emissivity control, in whichnanoparticles 610 driven to the surface of a melt 630 form a layer 680with a different conductivity or emissivity than the underlying,solidified material 650. The powder particles 600 may include ceramic,metal, polymer, glass, or combinations thereof. Nanoparticles 610 mayinclude metal, ceramic, polymer, carbon, or combinations thereof.

FIG. 6B is a schematic illustration of semi-passive solidificationcontrol including conductivity or emissivity control, in whichnanoparticles 610 remain distributed in the melt 630 and change theconductivity of the melt 630 and the final solid material 650. Again,the powder particles 600 may include ceramic, metal, polymer, glass, orcombinations thereof. Nanoparticles 610 may include metal, ceramic,polymer, carbon, or combinations thereof.

Thermal conductivity or emissivity control of solidification may utilizenanoparticles/microparticles or surface coatings which are higher inthermal conductivity compared to the base material. Thenanoparticles/microparticles or surface coatings may be incorporatedinto the melt, or may be rejected, such as to grain boundaries or to thesurface of the melt. The nanoparticles/microparticles or surfacecoatings may be miscible or immiscible with the molten state. Thenanoparticles/microparticles or surface coatings may be miscible orimmiscible with the final solid state.

Thermal conductivity or emissivity control of solidification may utilizenanoparticles/microparticles or surface coatings which are lower inthermal conductivity compared to the base material.

Thermal conductivity or emissivity control of solidification may utilizenanoparticles/microparticles or surface coatings which are higher inemissivity compared to the base material.

Thermal conductivity or emissivity control of solidification may utilizenanoparticles/microparticles or surface coatings which are lower inemissivity compared to the base material.

In some embodiments, the functionalization material may react withcontaminants in the melt (e.g., Mg—Ti—O system). When thefunctionalization material is properly chosen, the reacted material maybe selected such that the formed reaction product has a high surfacetension with the liquid, such that it may be rejected to the surface.The rejected reaction product may take the form of an easily removablescale. Optionally, the rejected layer is not actually removed but ratherincorporated into the final product. The rejected layer may manifestitself as a hard-facing carbide, nitride, or oxide coating, a softanti-galling material, or any other functional surface which may improvethe desired properties of the produced material. In some cases, therejected surface layer may be of a composition and undergo a coolingregime which may result in an amorphous layer on the surface of thesolidified material. These surface-rejected structures may result inimproved properties related to, but not limited to, improved corrosionresistance, stress corrosion crack resistance, crack initiationresistance, overall strength, wear resistance, emissivity, reflectivity,and magnetic susceptibility.

FIG. 7A is a schematic illustration of semi-passive solidificationcontrol including contaminant removal and rejection to the surface. Thepowder particles 700 may include ceramic, metal, polymer, glass, orcombinations thereof. Nanoparticles 710 may include metal, ceramic,polymer, carbon, or combinations thereof. Nanoparticles 710 aredistributed in a melt 730 and react with contaminants (not shown) fromthe melt 730, to form new nanoparticles/microparticles 785. The reactedcontaminants may be rejected to the surface of the final material 750 asa surface layer 790, for example.

FIG. 7B is a schematic illustration of semi-passive solidificationcontrol including contaminant reaction, in which the reactedcontaminants remain in the solid. Nanoparticles 710 are distributed in amelt 730 and react with contaminants (not shown) from the melt 730, toform new nanoparticles/microparticles 785. The reacted contaminants 785may remain in the solid 750. Again, the powder particles 700 may includeceramic, metal, polymer, glass, or combinations thereof. Nanoparticles710 may include metal, ceramic, polymer, carbon, or combinationsthereof.

Through contaminant removal or rejection, several scenarios arepossible. Nanoparticles/microparticles or surface coatings that reactwith or bind to undesired contaminants may be incorporated into thesolidification, in the same phase or a separate solid phase. The reactednanoparticles/microparticles or surface coatings may be rejected duringsolidification. When portions or select elements present in thenanoparticles/microparticles or coatings react with or bind tocontaminants, such portions or elements may be incorporated and/orrejected.

In some embodiments, the functionalized surface reacts upon heating toform a lower-melting-point material compared to the base material, suchas through a eutectic reaction. The functionalized surface may be chosenfrom a material which reacts with the underlying powder to initiatemelting at the particle surface, or within a partial volume of theunderlying powder. A heat source, such as a laser or electron beam, maybe chosen such that the energy density is high enough to initiate thesurface reaction and not fully melt the entire functionalized powder.This results in an induced uniform liquid phase sintering at theparticle surface. Upon freezing, the structure possesses acharacteristic microstructure indicating different compositions andgrain nucleation patterns around a central core of stock powder with amicrostructure similar to the stock powder after undergoing a similarheat treatment. This structure may later be normalized or undergopost-processing to increase density or improve the properties.

Another possible reaction is a peritectic reaction in which onecomponent melts and this melted material diffuses into a secondnanoparticle or microparticle, to form an alloyed solid. This newalloyed solid may then act as a phase-nucleation center, or may limitmelting just at the edge of particles.

FIG. 3 is a schematic illustration of semi-passive solidificationcontrol including peritectic reactions. The powder particles 300 mayinclude ceramic, metal, polymer, glass, or combinations thereof.Nanoparticles 310 may include metal, ceramic, polymer, carbon, orcombinations thereof. In FIG. 3, nanoparticles 310 are distributed in amelt 330. At elevated temperatures, the nanoparticles 310 dissolve toform a melt 340. Upon cooling, peritectic reactions take place, leadingto nanoparticle formation of dispersoids 340 in a melt 350.

Incorporating nanoparticles into a molten metal may be challenging whenthe nanoparticles have a thin oxide layer at the surface, since liquidmetals typically do not wet oxides well. This may cause thenanoparticles to get pushed to the surface of the melt. One way toovercome the oxide layer on nanoparticles, and the associatedwettability issues, is to form the nanoparticles in situ during meltpool formation. This may be achieved by starting with nanoparticles ofan element that forms an intermetallic with one component of the basealloy, while avoiding dissolution of the nanoparticles in the melt.Alternatively, binary compound nanoparticles that disassociate atelevated temperatures, such as hydrides or nitrides, may be used sincethe disassociation reaction annihilates any oxide shell on thenanoparticle.

As noted above, the surface functionalization may be designed to bereacted and rejected to the surface of the melt pool. In embodimentsemploying additive manufacturing, layered structures may be designed. Insome embodiments, progressive build layers and hatchings may be heatedsuch that each sequential melt pool is heated long enough to reject thesubsequent rejected layer, thereby producing a build with an externalscale and little to no observable layering within the build of therejected materials. In other embodiments, particularly those whichresult in a functional or desired material rejected to the surface,heating and hatching procedures may be employed to generate a compositestructure with a layered final product. Depending on the buildparameters, these may be randomly oriented or designed, layeredstructures which may be used to produce materials with significantlyimproved properties.

FIG. 4 is a schematic illustration of semi-passive solidificationcontrol in which a melt 430 solidifies with limited movement ofassembled nanoparticles 410, thereby allowing the nanoparticles 410 toorient in a three-dimensional structure (plurality of nanoparticles 410in solidified material 460) which repeats throughout the final solidmaterial 460. The powder particles 400 may include ceramic, metal,polymer, glass, or combinations thereof. Nanoparticles 410 may includemetal, ceramic, polymer, carbon, or combinations thereof.

Architected microstructures may be designed in which feature sizes(e.g., distance between nanoparticle nodes) within the three-dimensionalnetwork are selected, along with targeted compositions, for an intendedpurpose. Similarly, layered composite structures may be designed inwhich feature sizes (e.g., layer thicknesses or distance between layers)are selected, along with targeted compositions, for an intended purpose.

Note that rejection to the surface is not necessarily required togenerate layered structures. Functionalized surfaces may be relativelyimmobile from their initial position on the surface of the base powder.During melting, these functionalized surfaces may act as nucleationsites, as previously mentioned; however, instead of absorption into themelt, they may initiate nucleation at the location which was previouslyoccupied by the powder surface and is not molten. The result is afine-grained structure evolving from the surface nucleation source,towards the center. This may result in a designed composite structurewith enhanced properties over the base material. In general, thismechanism allows for the ability to control the location of desiredinclusions through controlled solidification.

In the additive manufacturing of titanium alloys, the problem ofmicrostructural texturing of subsequent layers of molten metals inducesanisotropic microstructures and thus anisotropic structural properties.Dispersing stable ceramic nanoparticles in the solidifying layers mayproduce grain structures with isotropic features which are stable uponrepetitive heating cycles. An example is a stable high-temperatureceramic nanoparticle, such as Al₂O₃ or TiCN attached to the surface of aTi-6Al-4V microparticle powder which is subsequently melted, solidified,and then reheated as the next layer of powder is melted on top. Theceramic nanoparticles can induce nucleation of small grains and preventcoarse grains from forming in the direction of the thermal gradient.

Any solidification control method which derives its primaryfunctionality from the surface functionalization of a powdered materialcan be considered in the scope of this invention. Other methods ofcontrol may include multiple types of control described above. Anexample of a combination of methods includes utilizing rejection to thesurface, internal reaction, along with emissivity control. For instance,a part may be processed using additive manufacturing in which afunctionalization material is selected to be dissolved into the surface,and reacts to form an insoluble material which is rejected to thesurface of the melt pool. This rejected material may then have a lowemissivity, which reflects any additional laser radiation, therebydecreasing the local heating and cooling the material quickly to controlsolidification. The resulting structure is a material with a controlledsolidification structure with a low-emissivity surface coating.

In some embodiments, the solid state is a three-dimensionalmicrostructure containing the nanoparticles and/or microparticles asinclusions distributed throughout the solid state.

In some embodiments, the solid state is a layered microstructurecontaining one or more layers comprising the nanoparticles and/ormicroparticles.

The method may further include creating a structure through one or moretechniques selected from the group consisting of additive manufacturing,injection molding, pressing and sintering, capacitive dischargesintering, and spark plasma sintering. The present invention provides asolid object or article comprising a structure produced using such amethod.

FIG. 8 is a schematic illustration of surface melting of afunctionalized powder particle 800, in which heat is applied and thenanoparticles 810 react with the surface to form a melt in a volume 810(outer region of particle) that is less than 100% of the particle 800volume. The powder particles 800 may include ceramic, metal, polymer,glass, or combinations thereof. Nanoparticles 810 may include metal,ceramic, polymer, carbon, or combinations thereof.

Some variations provide a structure created from the functionalizedpowder via additive manufacturing. The functionalized powder (withnanoparticles/microparticles or surface coating) may be incorporatedinto the final structure. In some embodiments, thenanoparticles/microparticles or surface coating are rejected, creating ascale. The scale may be unbonded to the structure. In some embodiments,the scale bonds to the structure or otherwise cannot be readily removed.This may be advantageous, such as to provide a structuralenhancement—for instance, rejected ceramic particles may add a hardfacing to the final structure. Rejected nanoparticles/microparticles orsurface coating may form a multilayer composite, wherein each layer hasa different composition. In some embodiments, rejectednanoparticles/microparticles or surface coating forms a spatiallyvariant composition within the bulk of the structure. Athree-dimensional architecture may also develop in the finalmicrostructure.

FIG. 9 is a schematic illustration of the formation of a layeredcomposite structure, in which a functionalized powder 900 having twodifferent types of nanoparticles 910, 915 leads to different particlesegregation, resulting in a layered structure having layers 970, 980,990. The powder particles 900 may include ceramic, metal, polymer,glass, or combinations thereof. Nanoparticles 910, 915 may includemetal, ceramic, polymer, carbon, or combinations thereof. In theschematic of FIG. 9, layer 970 results from nanoparticles 910 (orreactions thereof), layer 980 results from powder particles 900 (orreactions thereof), and layer 990 results from nanoparticles 915 (orreactions thereof).

Some variations provide a solid object or article comprising at leastone solid phase (i) containing a powdered material as described, or (ii)derived from a liquid form of a powdered material as described. Thesolid phase may form from 0.25 wt % to 100 wt % of the solid object orarticle, such as about 1 wt %, 5 wt %, 10 wt %, 25 wt %, 50 wt %, or 75wt % of the solid object or article, for example.

Other variations of the invention provide a solid object or articlecomprising a continuous solid phase and a three-dimensional network ofnanoparticle and/or microparticle inclusions distributed throughout thecontinuous solid phase, wherein the three-dimensional network blocks,impedes, or redirects dislocation motion within the solid object orarticle.

In some embodiments, the nanoparticle and/or microparticle inclusionsare distributed uniformly throughout the continuous solid phase. Thenanoparticle and/or microparticle inclusions may be present at aconcentration from about 0.1 wt % to about 50 wt % of the solid objector article, such as about 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, or 45 wt%, for example.

The nanoparticles and/or microparticles have an average maximum particledimension from about 1 nanometer to about 100 microns. In someembodiments, the average maximum particle dimension is less than 100nanometers. In these or other embodiments, the nanoparticles and/ormicroparticles have an average minimum particle dimension from about 1nanometer to about 1 micron, such as less than 100 nanometers. By“average maximum particle dimension” it is meant the number average ofthe maximum particle dimensions across all the nanoparticles and/ormicroparticles present. By “average minimum particle dimension” it ismeant the number average of the minimum particle dimensions across allthe nanoparticles and/or microparticles present. A perfect sphere has asingle dimension, the diameter, which is both the minimum and maximumparticle dimension. A cylinder has two characteristic length scales: thelength (height) and the diameter. When the cylinder is in the form of along rod, the maximum particle dimension is the length and the minimumparticle dimension is the diameter. In various embodiments, thenanoparticles and/or microparticles may have an average maximum particledimension of about, or less than about, 10, 25, 50, 75, 100, 150, 200,250, 300, 400, 500, 600, 700, 800, 900, or 1000 nanometers. In variousembodiments, the nanoparticles and/or microparticles may have an averageminimum particle dimension of about, or less than about, 5, 10, 25, 50,75, 100, 150, 200, 250, 300, 400, or 500 nanometers.

The solid phase may be fabricated from a first material selected fromthe group consisting of ceramic, metal, polymer, glass, and combinationsthereof. The nanoparticles and/or microparticles may be fabricated froma second material selected from the group consisting of metal, ceramic,polymer, carbon, and combinations thereof. The second material may bethe same as or different than the composition of the solid phase.

In some embodiments, light elements are incorporated into the system.For example, the particle surface (or the surface of nanoparticles ormicroparticles present on the powder particles) may be surface-reactedwith an element selected from the group consisting of hydrogen, oxygen,carbon, nitrogen, boron, sulfur, and combinations thereof. For example,reaction with hydrogen gas may be carried out to form a metal hydride.Optionally, the particle or a particle coating further contains a salt,carbon, an organic additive, an inorganic additive, or a combinationthereof. Certain embodiments utilize relatively inert carbides that areincorporated (such as into steel) with fast melting and solidification.

Methods of producing surface-functionalized powder materials aregenerally not limited and may include immersion deposition, electrolessdeposition, vapor coating, solution/suspension coating of particles withor without organic ligands, utilizing electrostatic forces and/or Vander Waals forces to attach particles through mixing, and so on. U.S.patent application Ser. No. 14/720,757 (filed May 23, 2015), U.S. patentapplication Ser. No. 14/720,756 (filed May 23, 2015), and U.S. patentapplication Ser. No. 14/860,332 (filed Sep. 21, 2015), each commonlyowned with the assignee of this patent application, are herebyincorporated by reference herein. These disclosures relate to methods ofcoating certain materials onto micropowders, in some embodiments.

For example, as described in U.S. patent application Ser. No.14/860,332, coatings may be applied using immersion deposition in anionic liquid, depositing a more-noble metal on a substrate of a lessnoble, more electronegative metal by chemical replacement from asolution of a metallic salt of the coating metal. This method requiresno external electric field or additional reducing agent, as withstandard electroplating or electroless deposition, respectively. Themetals may be selected from the group consisting of aluminum, zirconium,titanium, zinc, nickel, cobalt copper, silver, gold, palladium,platinum, rhodium, titanium, molybdenum, uranium, niobium, tungsten,tin, lead, tantalum, chromium, iron, indium, rhenium, ruthenium, osmium,iridium, and combinations or alloys thereof.

Organic ligands may be reacted onto a metal, in some embodiments.Organic ligands may be selected from the group consisting of aldehydes,alkanes, alkenes, silicones, polyols, poly(acrylic acid),poly(quaternary ammonium salts), poly(alkyl amines), poly(alkylcarboxylic acids) including copolymers of maleic anhydride or itaconicacid, poly(ethylene imine), poly(propylene imine),poly(vinylimidazoline), poly(trialkylvinyl benzyl ammonium salt),poly(carboxymethylcellulose), poly(D- or L-lysine), poly(L-glutamicacid), poly(L-aspartic acid), poly(glutamic acid), heparin, dextransulfate, l-carrageenan, pentosan polysulfate, mannan sulfate,chondroitin sulfate, and combinations or derivatives thereof.

The reactive metal may be selected from the group consisting of alkalimetals, alkaline earth metals, aluminum, silicon, titanium, zirconium,hafnium, zinc, and combinations or alloys thereof. In some embodiments,the reactive metal is selected from aluminum, magnesium, or an alloycontaining greater than 50 at % of aluminum and/or magnesium.

Some possible powder metallurgy processing techniques that may be usedinclude but are not limited to hot pressing, low-pressure sintering,extrusion, metal injection molding, and additive manufacturing.

The final article may have porosity from 0% to about 75%, such as about5%, 10%, 20%, 30%, 40%, 50%, 60%, or 70%, in various embodiments. Theporosity may derive from space both within particles (e.g., hollowshapes) as well as space outside and between particles. The totalporosity accounts for both sources of porosity.

The final article may be selected from the group consisting of asintered structure, a coating, a weld filler, a billet, a net-shapepart, a near-net-shape part, and combinations thereof. The article maybe produced from the coated reactive metal by a process comprising oneor more techniques selected from the group consisting of hot pressing,cold pressing, sintering, extrusion, injection molding, additivemanufacturing, electron-beam melting, selective laser sintering,pressureless sintering, and combinations thereof.

In some embodiments of the invention, the coated particles are fusedtogether to form a continuous or semi-continuous material. As intendedin this specification, “fused” should be interpreted broadly to mean anymanner in which particles are bonded, joined, coalesced, or otherwisecombined, at least in part, together. Many known techniques may beemployed for fusing together particles.

In various embodiments, fusing is accomplished by sintering, heattreatment, pressure treatment, combined heat/pressure treatment,electrical treatment, electromagnetic treatment, melting/solidifying,contact (cold) welding, solution combustion synthesis, self-propagatinghigh-temperature synthesis, solid state metathesis, or a combinationthereof.

“Sintering” should be broadly construed to mean a method of forming asolid mass of material by heat and/or pressure without melting theentire mass to the point of liquefaction. The atoms in the materialsdiffuse across the boundaries of the particles, fusing the particlestogether and creating one solid piece. The sintering temperature istypically less than the melting point of the material. In someembodiments, liquid-state sintering is used, in which some but not allof the volume is in a liquid state.

When sintering or another heat treatment is utilized, the heat or energymay be provided by electrical current, electromagnetic energy, chemicalreactions (including formation of ionic or covalent bonds),electrochemical reactions, pressure, or combinations thereof. Heat maybe provided for initiating chemical reactions (e.g., to overcomeactivation energy), for enhancing reaction kinetics, for shiftingreaction equilibrium states, or for adjusting reaction networkdistribution states.

Some possible powder metallurgy processing techniques that may be usedinclude, but are not limited to, hot pressing, sintering, high-pressurelow-temperature sintering, extrusion, metal injection molding, andadditive manufacturing.

A sintering technique may be selected from the group consisting ofradiant heating, induction, spark plasma sintering, microwave heating,capacitor discharge sintering, and combinations thereof. Sintering maybe conducted in the presence of a gas, such as air or an inert gas(e.g., Ar, He, or CO₂), or in a reducing atmosphere (e.g., H₂ or CO).

Various sintering temperatures or ranges of temperatures may beemployed. A sintering temperature may be about, or less than about, 100°C., 200° C., 300° C., 400° C., 500° C., 600° C., 700° C., 800° C., 900°C., or 1000° C.

A sintering temperature is preferably less than the reactive-metalmelting temperature. In some embodiments, a sintering temperature may beless than a maximum alloy melting temperature, and further may be lessthan a minimum alloy melting temperature. In certain embodiments, thesintering temperature may be within the range of melting points for aselected alloy. In some embodiments, a sintering temperature may be lessthan a eutectic melting temperature of the particle alloy.

At a peritectic decomposition temperature, rather than melting, a metalalloy decomposes into another solid compound and a liquid. In someembodiments, a sintering temperature may be less than a peritecticdecomposition temperature of the metal alloy. If there are multipleeutectic melting or peritectic decomposition temperatures, a sinteringtemperature may be less than all of these critical temperatures, in someembodiments.

In some embodiments pertaining to aluminum alloys employed in themicroparticles, the sintering temperature is preferably selected to beless than about 450° C., 460° C., 470° C., 480° C., 490° C., or 500° C.The decomposition temperature of eutectic aluminum alloys is typicallyin the range of 400-600° C. (Belov et al., Multicomponent PhaseDiagrams: Applications for Commercial Aluminum Alloys, Elsevier, 2005),which is hereby incorporated by reference herein.

A solid article may be produced by a process selected from the groupconsisting of hot pressing, cold pressing and sintering, extrusion,injection molding, additive manufacturing, electron beam melting,selected laser sintering, pressureless sintering, and combinationsthereof. The solid article may be, for example, a coating, a coatingprecursor, a substrate, a billet, a net shape part, a near net shapepart, or another object.

The present invention is applicable to additive manufacturing andwelding applications, along many other applications. Some embodimentsprovide powder metallurgy processed parts that are equivalent tomachined parts. Some embodiments provide surface coatings that resistcorrosion, which coatings are formed during the part fabrication insteadof as an extra step.

Other commercial applications include, but are not limited to, complexcomponent integration (reduce number of individual parts used to makeone assembly), reduced-weight optimized structures, battery and fuelcell electrodes, catalyst materials, lightweight fillers, complextooling, and improved performance of existing parts.

In this detailed description, reference has been made to multipleembodiments and to the accompanying drawings in which are shown by wayof illustration specific exemplary embodiments of the invention. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention, and it is to be understood thatmodifications to the various disclosed embodiments may be made by askilled artisan.

Where methods and steps described above indicate certain eventsoccurring in certain order, those of ordinary skill in the art willrecognize that the ordering of certain steps may be modified and thatsuch modifications are in accordance with the variations of theinvention. Additionally, certain steps may be performed concurrently ina parallel process when possible, as well as performed sequentially.

All publications, patents, and patent applications cited in thisspecification are herein incorporated by reference in their entirety asif each publication, patent, or patent application were specifically andindividually put forth herein.

The embodiments, variations, and figures described above should providean indication of the utility and versatility of the present invention.Other embodiments that do not provide all of the features and advantagesset forth herein may also be utilized, without departing from the spiritand scope of the present invention. Such modifications and variationsare considered to be within the scope of the invention defined by theclaims.

What is claimed is:
 1. A powdered material comprising a plurality ofparticles, wherein said particles are fabricated from a first material,wherein each of said particles has a particle surface area that issurface-functionalized with a second material containing nanoparticlesand/or microparticles, wherein said second material is different thansaid first material, wherein the melting point of said second materialis higher than the melting point of said first material, and whereinsaid nanoparticles and/or microparticles are selected for epitaxial fitof crystal lattice parameters with said first material.
 2. The powderedmaterial of claim 1, wherein said first material is selected from thegroup consisting of ceramic, metal, polymer, glass, and combinationsthereof.
 3. The powdered material of claim 1, wherein said secondmaterial is selected from the group consisting of metal, ceramic,polymer, carbon, and combinations thereof.
 4. The powdered material ofclaim 1, characterized in that on average at least 1% of said particlesurface area is surface-functionalized with said nanoparticles and/orsaid microparticles.
 5. The powdered material of claim 1, wherein saidparticles are present as a loose powder, a paste, a suspension, a greenbody, or a combination thereof.
 6. The powdered material of claim 1,wherein said particles have an average particle size from about 1 micronto about 1 centimeter.
 7. The powdered material of claim 1, wherein saidnanoparticles and/or microparticles have an average maximum particledimension from about 1 nanometer to about 100 microns.
 8. The powderedmaterial of claim 1, wherein said nanoparticles and/or microparticleshave an average minimum particle dimension from about 1 nanometer toabout 1 micron.
 9. The powdered material of claim 1, wherein saidnanoparticles and/or microparticles are nucleation sites within saidpowdered material.
 10. The powdered material of claim 1, wherein saidnanoparticles and/or microparticles are characterized by an averagediameter that is less than 20% of an average diameter of said particles.11. The powdered material of claim 1, wherein said second material is inthe form of an intermittent coating.